This invention is primarily applicable to the concentration by flotation of hydrated aluminum oxide minerals from such materials as Bauxites, Bauxitic Clays, and Laterites.
Heretofore the sole source of raw materials for the production of aluminum metal in the United States was Bauxites. The high grade hydrated aluminum oxide mineral concentrates produced by the present invention even from low grade raw materials, will now be able to satisfactorily replace Bauxite as feed to the Bayer process, which is universally the initial processing step in the manufacture of aluminum metal. Currently, American aluminum companies depend upon foreign sources for approximately 85% of the feed to their Bayer processes. Reserves of economically usable Bauxite in the United States are dwindling rapidly and the dependence on foreign sources is increasing accordingly. In the United States there are large tonnages of low grade hydrated aluminum oxide bearing materials for which heretofore no economic process existed for their use in making aluminum. For instance, there are reportedly several hundred million tons of hydrated aluminum oxide mineral-bearing laterites in the states of Oregon and Washington alone. With the application of the invention to this type of material an aluminum oxide concentrate can be produced that is at least equal in aluminum mineral content to Jamaican Bauxite, and at an appreciably indicated lower cost. Currently, Jamaican Bauxite is one of the major source supplies of the American aluminum industry. It is obvious that for the first time in a long number of years the process of the invention can place the United States aluminum industry in the position of being independent of foreign sources for their raw material requirements.
Research in concentration of Bauxites has been carried out by the U.S. Bureau of Mines over a long period of years. The published data from the U.S. Bureau of Mines is in the U.S. Bureau of Mines publications known as R. I.'s going back as far as 1927. In a pilot plant designed and intermittently operated by the U.S. Bureau of Mines from 1945 until about 1949, the circuit consisted of gravity concentration, flotation and magnetic cobbing of the final flotation concentrate. Both slimes and soluble salts proved to be major problems.
In the case of the slimes, everything possible was done to minimize their formation. Even under such conditions, where an ore tended to slime, either recovery and grade of concentrate produced or both were generally commercially unacceptable. No answer to the problem was found.
In the case of the soluble salts, zeolite-treated water was used in the flotation circuit to precipitate the soluble salts contained in the water supply.
The inventor has been informed that the only plant that has been placed in operation in recovering hydrated aluminum oxide minerals by flotation was in Guyana, which used screening and thorough desliming of the ore prior to flotation. Due to the fine grained nature of the United States deposits of low grade Bauxites, Bauxitic Clays and Laterites, if such a process was applied to any of these materials, the resulting loss of the hydrated aluminum oxide minerals contained in the slime fraction of the deslimed ores would be so high as to make the process uneconomic due to the resultant low recovery.
In the process of my invention, I have been able to obtain outstanding metallurgical results both as to recovery and grade of concentrates in treating low grade Bauxites and Bauxitic Clays from deposits located in the United States, using my flotation process either alone or in combination with magnetic cobbing.
No desliming of the ore is required prior to my flotation stages and most surprisingly the process can be carried out without prior treatment of the water used in the process. Similarly, in using essentially the same flotation circuit, the hydrated aluminum oxide minerals were successfully floated from United States Laterite deposits. To the inventor's knowledge, this is the first time that any process has been successfully applied to the concentration of the alumina bearing minerals from such deposits.